The present invention relates to a device installed in a copier for selecting a magnification.
Two different kinds of devices are available for the selection of a magnification, as well known in the art. In one of them, a plurality of magnifications which vary stepwise are set beforehand so that any one of them may be selected by an operator at the time of copying operation. Since it is a common practice to copy documents of definite formats on paper sheets of definite formats, the above-mentioned stepwise magnifications, or fixed magnifications, are often set in terms of ratios between the definite formats. For example, assuming documents and paper sheets which belong to an A and a B format series, fixed magnifications may be predetermined as shown in Table 1 below.
TABLE 1 ______________________________________ DOCUMENT PAPER A3 A4 A5 B4 B5 ______________________________________ A3 1.000 1.414 2.000 1.154 1.632 A4 0.707 1.000 1.414 0.816 1.154 A5 0.500 0.707 1.000 0.576 0.813 B4 0.865 1.224 1.733 1.000 0.576 B5 0.612 0.865 1.224 0.706 1.000 ______________________________________ A3 297 .times. 420 mm A4 210 .times. 297 mm A5 148 .times. 210 mm B4 257 .times. 364 mm B5 182 .times. 257 mm
As shown in Table 1, when a document of format A3 is to be copied on a paper sheet of format A4, the magnification is 0.707. Likewise, when a document of format B4 is to be copied on a paper sheet of format A3, the magnification is 1. 154.
Another format system commonly adopted includes a letter (LT) size, a legal (LG) size, a double letter (DLT) size, and a half-letter (HLT) size. For such a format system, fixed magifications shown in Table 2 below may be contemplated.
TABLE 2 ______________________________________ DOCUMENT PAPER LT LG DLT HLT ______________________________________ LT 1.000 0.786 0.647 1.294 LG 1.000 1.000 0.773 1.545 DLT l.294 1.214 1.000 2.000 HLT 0.647 0.607 0.500 1.000 ______________________________________ LT LETTER 81/2" .times. 11" (inch) LG LEGAL 81/2" .times. 14 DLT DOUBLELETTER 11" .times. 17 HLT HALFLETTER 51/2" .times. 81/2
The prior art device of the type having some stepwise fixed magnifications as stated above involves difficulty in practical use, however. Specifically, in order that all of the fixed magnifications such as those shown in Table 1 or 2 may be selectively set up, a different button which corresponds to each magnification has to be provided on an operation board of a copier. In addition, it is troublesome for a person to select a particular button out of such a great number of buttons.
The other type of prior art magnification selecting device allows the magnification to be changed continuously in a stepless fashion. Although this type of device eliminates the need for numerous buttons as discussed above and frees a person from troublesome button selection, it brings about another drawback that a person has to accurately set up such precise magnifications as those shown in Table 1 or 2 in the event of a change of magnification between definite formats. Usually, therefore, stepwise magnifications are preferred rather than stepless magnifications.